The ratio of excimer to monomer emission intensities, denoted by I-D/I-M, was measured for Py - COO(CH2CH2O)(m)CO - Py, where Py denotes the 1-pyrenyl group and m = 1-4, in solvents of different viscosity, 17. Three different systems were used to change the viscosity of the medium : (a) Mixtures of methanol and ethylene glycol at 25 degrees C, (b) linear aliphatic alcohols, H(CH2)(n)OH, where n = 1-6, also at 25 degrees C, and (c) ethylene glycol over the range 6.6-35 degrees C. The ratio I-D/I-M decreases sharply as eta increases, and the rate of the decrease in I-D/I-M is a function of m. Quantitatively, the dependence of I-D/I-M on eta at high viscosity, i.e., the slope [d(I-D/I-M)/d(1/eta)](infinity), is larger in the present work than in another series of 1-pyrenyl diesters in which the flexible spacer is an oligomer of polyethylene, instead of an oligomer of polyoxyethylene. In the limit where eta --> infinity, the ratio I-D/I-M assumes its largest value in the bichromophoric compound with n = 2. However, as eta decreases the compound with m = 3 becomes the one with the largest I-D/I-M. A complete rotational isomeric state analysis (for the compounds with m = 1-3) and a Monte Carlo simulation (for the compound m = 4) of the conformations of the diesters can rationalize the behavior of I-D/I-M in the high viscosity limit.